Motor fuels



fiatented Get. 8, 1946 MOTOR FUELS llaul L. De Verter, Baytown, Tex.,assignor to Standard Oil Development Company, a corporation of DelawareNo Drawing. Application December 3, 1943, Serial No. 512,781

'2 Claims.

This invention relates to novel motor fuels and methods of preparing thesame, and more particularly it relates to the preparation of stable highoctane motor fuels especially adapted for aviation use.

In the preparation of high octane motor fuels lead tetraethyl is often,if not generally, used to raise the octane number of a hydrocarbonliquid boiling in the gasoline boiling range. However, the storage ofcertain types of gasoline base stocks containing tetraethyl lead hasresulted in the formation of a haze or precipitate in the gasoline,particularly when such fuels are stored at relatively elevatedatmospheric temperatures, such as in tropical climates, especially whenextended storage periods are involved. The problem has been most seriousand perplexing in cases in which the precipitate formed during storagecontains only a relatively small proportion of gum, i. e. small enoughto pass even fairly strict motor fuel specifications, but contains amajor proportion of lead, chiefly in the form of lead oxide, whichapparently results from the decomposition of the tetraethyl lead.Although the actual amount of tetraethyl lead lost by such decompositionduring storage is sometimes small, and, perhaps, entirely negligible,from the point of view of the loss in octane rating, nevertheless theformation of the lead-containing precipitate is serious because evensmall amounts of such a precipitate tend to clo the strainers in theaviation motor fuel system and it may, therefore, cause faulty operationof the airplane motors.

Although in certain instances formation of a gummy precipitate hasappeared to be accelerated in some types of gasoline base stocks,especially cracked gasolines, in the presence of tetraethyl lead, theaddition of any of a large number of gum inhibitors was found toovercome such accelerated gum formation; but the present inventioninvolves a very different problem because the precipitate formed in thecases with which this invention is involved contains only a small andunobjectionable amount of gum but contains a large proportion of lead.This invention is likewise not related to the problem of discolorationof certain types of gasoline base stocks, even straight-run petroleumdistillates, when exposed to sunlight, either when such fuels containtetraethyl lead or not, because such discoloration is primarily due tochemical changes in some of the organic substituents of the gasolinebase stock; whereas in the fuels with which the present invention isconcerned there is not substantial discoloration of the base stock andthe problem appears to be solely, or at least primarily, one ofdecomposition of the tetraethyl lead per se, most of the storage beingin the dark.

In extensive studies which led to the present invention it was foundthat straight-run gasoline distillates from highly aromatic crudepetroleums could be leaded, i. e., have tertaethyl lead added thereto,and stored without formation of objectionable amounts of lead-containingprecipitate. On the other hand, it was found that gasoline base stocksconsisting substantially or entirely of aliphatic hydrocarbons, whethernatural or synthetic, but particularly synthetic gasoline base stocksmade by alkylation, for instance, of butylenes with isobutane, whenleaded and stored, resulted in formation of undesirably high amounts ofprecipitate containing a major proportion of lead oxide. Furthermore, itwas found that most of the chemical compounds usually used as guminhibitors would not prevent such decomposition of the tetraethyl lead.

Although the explanation of these peculiar phenomena is not known withcertainty, it is believed that the chief reason why the problem ofdecomposition of the tetraethyl lead during storage has not becomeserious until recently may be due to the possible presence of somenatural stabilizer present in cracked gasolines and in straight-rundistillates obtained from aromatic crudes.

The primary object of the present invention is to stabilize such leadedfuels which are normally unstable with respect to formation of aprecipitate containin a major proportion of lead during storage.

Broadly, the invention comprises adding a small amount of hydroxyaromatic hydrocarbon of the hydroquinone class to such motor fuels whichare normally unstable with respect to formation of a haze or precipitateand containing a major proportion of lead during storage. Hydroquinone,p--HO-CsH4-OH, itself has been found to be a most effective stabilizer,although other compounds within the hydroquinone class may be used, suchas quinhydrone, CsHiOaCeH4(OH) 2, which may be considered as a, quinonesubstituent of hydroquinone.

The amount of stabilizer to be used will va y to some extent accordingto the particular requirement of the gasoline base stock being used andaccording to the severity of the conditions under which the motor fuelis to be stored, but normally it will range between the approximatelimits of .05-.5 lb. of stabilizer pe 1000 gallons of motor fuel, andpreferably about 0.1-0.3 lb./ 1000 gallons of fuel. This stabilizer isnot readily soluble in the gasoline base stocks in question and,therefore, should be added thereto in solution in alcohol or similarsolvent either at or near the time of adding the tetraethyl leadthereto. Instead of using tetraethyl lead in preparing the motor fuelsin question other lead alkyl known anti-knock agents may be used, suchas lead tetramethyl, lead dimethyl diethyl, etc. The amount of leadalkyl anti-knock agent to be used will, of course, vary primarily uponthe octane requirement of the finished blend, and accordingly may rangefrom relatively small amounts such as 0.5 or 1.0 cc./gal1on of fuel, upto relatively large amounts, such as 5 or 6 cc. or more per gallon, asmay sometimes be desired for super aviation fuels or other specialpurposes, but the invention is particularly applicable to motor fuelscontaining about 3 cc. or more of tetraethyl lead per gallon and isespecially applicable to aviation motor fuels now being used formilitary purpose which require 4 cc. of tetraethyl lead per gallon.

The hydrocarbon or gasoline base stock which, of course, forms the majorconstituent of the motor fuels in question may be composed of varioustypes of constituents as suggested above, but the invention isparticularly applicable to synthetic pure aliphatic hydrocarbon basestocks within the gasoline boiling range, such as those made byalkylation of normal olefins with isoparafiins. Such alkylates generallyhave an ASTM octane number of at least 80 and are substantiallysaturated in respect to hydrogen as shown by a bromine number test inthe range of 0.1 to 0.2 and an acid heat value in the range of 1 to 3 F.

In preparing alkylate base stock of the type preferred, known methods ofalkylation may be used, such as reacting isobutane with olefins, such asbutylenes or pentylenes or mixtures thereof, in the presence of sulfuricacid of about 90-100%, preferably 92-98%, concentration, at atemperature of about -100 F., preferably 4070 F. For instance, a liquidmixture consisting of about 58% by volume of isobutane and 20% by volumeof butylenes is fed into a reactor containing sulfuric acid of about 96%concentration, using about one volume of hydrocarbon feed per volume ofacid, and maintaining the temperature at about 40 F. and at a pressureof about 15 lbs/sq. in. gauge. After a reaction period of about 0.5 hourthe hydrocarbon layer is separated from the acid catalyst layer and iswashed successively with water, aqueous caustic, and water. In suchalkylation processes, in place of isobutane one may use otheriso-alkanes, such as isopentanes. Also, various oleflns may be used,such as isobutene, normal butene-2 or normal butene-3 or a mixturethereof, such as mentioned above, or one or more of the variouspentenes, such as pentene-2, pentene-3, or methyl-2-butene-3, or evenone or more of the normal hexenes or mixtures of normal olefins havingdifferent numbers of carbon atoms, such as 4 and 5 or 4, 5, and 6. It isto be understood, of course, that in such alkylation processes, one mayuse catalysts other than sulfuric acid such as phosphoric acid, hydrogenfluoride,-boron fluoride, etc.

In place of alkylates, such as described above, one may also usesynthetic aliphatic base stocks made by reacting normal olefin andiso-olefins in the presence of sulfuric acid and other suitablecatalysts; such reaction products are normally referred to ascopolymers. For instance, normal butylene, which may consist of normalbutene-2 or butene-3 or a mixture thereof, may be reacted withisobutylene in the presence of sulfuric acid of about 69 to 70%concentration, at a temperature of about 145 to 150 F. and under apressure of about 145 to 150 lbs/sq. in. above atmospheric. Theresulting copolymerization product is separated from the acid catalystand fractionated to recover a codimer, which is probably a mixture ofseveral branched octenes. Similarly other codimers may be prepared, suchas by reacting isobutylene with propylene or even ethylene or withhigher olefins, such as one or more of the pentenes or else higheriso-olefins, e. g. iso-pentene, may be reacted with some of the variouolefin's referred to. Since these codimers are generally not desirablefor use in aviation fuels in their unsaturated or olcfinic state, it ispreferable for maximum lead susceptibility and other aviation motor fuelcharacteristics, to hydrogenate the codimers to the correspondingbranched parafiins.

The invention also applies to natural petroleum fractions within thegasoline boiling range which consist substantially entirely of aliphatichydrocarbons, or fractions which are substantially entirely free, orhave been separated, from aromatic constituents, for instance, astraightrun gasoline distillate from a Pecos crude, which is anessentially isoparafiinic base stock, or an isopentane fractiondistilled or otherwise separated in substantially pure state from anydesired crude.

The invention applies to motor fuels comprising mixtures of thesevarious base stocks which are normally unstable in respect to formationof a precipitate containing lead during storage, if stored in the formof a leaded blend. For instance, in preparing high octane aviation motorfuels, especially for military purposes, it is often desired to use analkylate as the primar constituent of the motor fuel base stock, and touse a small amount of isopentane, isohexane, isoheptane or other lowboiling substantially pure aliphatic hydrocarbon, such as cyclopentane,in sufficient amount to make a blended fuel having the desired vaporpres-sure for ease of starting and for operation at suitably lowtemperatures.

Although the invention applies particularly to aviation motor fuel basestocks consisting substantially or entirely of aliphatic hydrocarbons,either natural or synthetic, as described above, it does not exclude theuse of other addition agents, particularly anti-knock agents consistingof other types of hydrocarbons or various oxygen, nitrogen, or otherderivatives thereof, provided that such addition agents do not consistof, or comprise, cracked petroleum fractions or mixed petroleumfractions obtained by straight-run distillation of aromatic-containingcrudes. In other words, the invention is not intended to apply to theuse of mixed aromatic fractions, such as may be obtained by solventextraction with liquid sulfur dioxide, etc., of aromatic type gasolinebase stocks; such mixed aromatic fractions, when loaded, do not needstabilization against decomposition of the tetraethyl lead duringstorage, and furthermore are more sufficiently high in octane number andlead susceptibility or octane blending value for the purposes of thepresent invention. On the other hand, synthetic or substantially puresingle aromatic compounds may be used, such as benzene, toluene,isopropyl benzene, tertiary butyl benzene, toluidine, xylidene, etc.Similarly, aliphatic oxygen-containing anti-knock agents may be used,such as di-isopropyl ether, ethyl isopropyl ether, isopropyl tertiarybutyl ether, isopropyl alcohol, ethyl alcohol, tertiary butyl alcohol,acetone, methyl isopropyl ketone, etc. These various anti-knock additionagents may be used in amounts ranging from about 1% to 40%, preferablyabout 5% to 20%, or 30%.

The invention and the advantages thereof will be better understood froma consideration of the following experimental data.

3 cc. of tetraethyl lead per gallon were added Test No. 1 shows that,without inhibitor, the to an isobutane-butylene alkylate which was madeleaded alkylate, containing 3 cc. of tetraethyl lead in commercialequipment that was operated subper gallon, when subjected to theaccelerated gum stantially according to conditions which have test,forms a brown precipitate and shows a previously been described. 29.7mg. total of lead plus gum, of which 16.3

The resulting fuel, which had an AS'IM octane mg. is lead and 13.4 mg.is gum. Tests Nos. number above 100 was then subjected to the 2 and 3show that the addition of .l and .2 lbs., accelerated gum test alone andwith addition of respectively, of hydroquinone per 1000 gallonshydrcquinone or quinhydrone in several concenof fuel, completelyprevents the formation of any trations. The accelerated gum testprocedure precipitate and reduces the gum to a satisfactorily used wasthat adopted by the Cooperative Fuel low amount, 2.6 mg. and 2.8 mg.(both below the Research Committee of the Society of Automotive allowedmaximum of 6 mg.) with no lead present Engineers, and published by thatcommittee in with the gum. Tests Nos. 4 and 5 show similarly TestProcedures and General Information in satisfactory results upon the useof quinhydrone Current Use in the Development and Utiliza- 5 in place ofhydroquinone.

tion of Aviation, Motor, and Automotive Diesel Another series of testswas made to obtain some Fuels, May 1941, page 15, and comprisedsubapproximate estimate of the probable duration jecting 200 ml. of themotor fuel sample to oxidaof the stability period, assuming bysubjecting tion for a period of 5 hours in a glass sample samples ofleaded fuel to the same accelerated bottle containing strips of carbonsteel having an gum test, except extending the time of oxidation area ofsquare inches. To be considered as from 5 hours to 10 hours, to seewhether the passing this test satisfactorily asample should notinhibited samples would have a predicted storform a precipitateexceeding 5 mgs. per 190 1 age stability life of over three yearsbecause the f Oxidized samme and the gum value Should not usual 5-hourtest oxidation period may be assumed exceed 6 per of Oxidized Samples 25to be equivalent to 18 months of actual storage. with deductionallowable for lead present in the In thls Series of motor f used wasgum. The sample to be submitted to the acceler loo'octane gasolme Whlchcontamed 3 of tetraethyl lead per gallon and the base stock ated gumtest must be protected from direct or I d1 fiuse d light prior to thetest. was composed of 7.2% 1sopentane,40% 1sobutane- L 3Q butylenealkylate, and 52.8% virgin naphtha from alkylate used when t wlthou" anyGulf Coast and Pecos crude oils. The motor fuel, teiraefihyl lead,Showed preclpltate and only before adding the tetraethyl lead had an A.P. 1. a very small, practically negligible, amount of gravity of 93 Reidvapor pressure of um, namely, about -2 in the accelflrated pounds persquare inch and an ASTM octane gum test, thereby indicating that thealkylate 5 number of 83. base stock per se is normally stable in respectto The results of the accelerated gum tests were precipitate or gumformation during storage. as follows:

TABLE 2 Effect of difierent oxidation test periods Time of TestPredicted storage N0. g fig Pb+gum Pb Gum stability life 1 WITHOUTINHIBITOR Mg. M'g. Mg. 6 5 Yellow 10. 7 Tr. 10.7 Less than 18 months. 710 do 36.8 13.8 23.0

, WITH .1 LB. HYDROQUINONE PER 1,000 GALLONS s 5 Non". 1.8 Nil 1.8 9 10..do... 2.3 Nil 2.3 Over3years.

WITH .1 LB. QUINHYDRONE PER 1,000 GALLONS l0 5 do. 2.0 Nil 2.0 11 10 do3.5 Nil 3.5 Over3years.

1 Assuming 6-hour oxidation period equivalent to 18 months storage. Theresults of the accelerated gum test on the The above tests in Table 2show that without leaded blends of this same alkylate are as follows:inhibitor (tests Nos. 6 and 7) a yellow precipi- TABLE 1 Accelerated gumtests Accelerated gum tests T. E. L. Inhibitor,

content lbs./l,000 gals.

Test N0. Sample IPpt. Pb-l-gum Pb Gum Cc. Mg. Ma. Mg.

3 0 Brown 29 7 16.3 13 4 3 .l hydroqumone. None 2.6 2 6 3 .2hydroquinone .do. 2. 8 2 8 3 .1 quinhydrone.. -do 1.8 l 8 3 .2quinhydrone do 2.0 2 0 tate is formed in both the and lo-hour'tests andthat the amount of lead plus gum increases from 10.7 at 5 hours to 36.8at hours, the amount of lead in the gum increasing from a trace at 5hours to 13.8 in 10 hours; whereas with .1 lb. hydroquinone per 1000gallons (tests Nos. 8 and 9) and with .1 lb. quinhydrone (tests Nos. 10and 11) no precipitate was formed even with the 10-hour oxidationperiod, and the amount of lead plus gum increased only slightly from 1.8to 2.3 in the case of hydroquinone and 2.0 to 3.5 in the case ofquinhydrone, both being considerably below the 6.0 maximum permitted,there being no lead present in the gummy residue called lead gums. Inother words, these tests indicate that .1 1b. of inhibitor per 1000gallons of leaded fuel is suflicient in the case of hydroquinone orquinhydrone to stabilize the fuel for over three years.

Another series of tests was made to determine the behavior of similarleaded fuel blends in actual storage over a long time, up to 18 months,making test observations at intermediate periods of 2, 4, 7, 10 and 12months. In this series of tests, the fuel used was the same as that usedfor tests 6 to 11 (Table 2) and contained 3 cc. of tetraethyl lead pergallon.

In this series of tests large samples were stored in contact with aniron strip (having a total area of 4 sq. inches) in brown glass bottlesenclosed in brown paper bags to prevent interfering effect of sunlight.After successive 2 months periods of storage, portions of the largesample were withdrawn and submitted to the accelerated gum tests. Duringthe latter storage periods, the accelerated gum tests were alsosupplemented gum test both without storage and at all periods up to the18 months, the fuel inhibited with hydroquinone (tests Nos. 19-25) didnot form any precipitate at any time throughout the 18-month test, andthe fuel inhibited with quinhydrone (tests Nos. 26-32) was stabilizedagainst precipitate formation throughout the 4-month period butdeveloped a slight brown or yellow precipitate during longer storageperiods. Also, as indicated in previous tests, the leaded fuel withoutinhibitor showed large amounts of lead plus gum ranging from 10.7initially to 30.4 at 18 months, in the accelerated gum tests, whereashydroquinone maintained the lead plus gum figure to a value rangingbetween 1.8 and 3.6, with no 166101 present, while the quinhydroneshowed satisfactory lead plus gum values, with no lead, for the first '7months. Thus the quinhydrone shows a substantial stabilizing effectagainst formation of a precipitate containing lead during storage,although hydroquinone is superior in stabilizing the leaded fuel for amuch longer period. The copper-dish and silica-dish gum tests indicatethat long-time storage of the leaded fuels did not have any substantialeffect on either the copper-dish gum or silica-dish gum.

As an indication that the invention applies not only to synthetichydrocarbon fuels such as made by alkylation, etc., but also to naturalsubstantially pure aliphatic hydrocarbons, it is noted that a sample ofisopentane when submitted to the accelerated gum test showed noprecipitate and only 1.1 gum when tested without tetraethyl lead, but,when tested with an addition of 3 cc. of tetraethyl lead per gallon,gave a heavy brown precipitate and 18.5 lead plus gum, the lead per seby copper-dish and silica-dish gum tests. being 16.3. It is thusapparent that although TABLE 3 Long-time storage tests Stora e Test No.b Copper time, Accelerated gum test months dish gum gililgfl gum I Ppt.Pb-l-gum Pb Gum WITHOUT INHIBITOR WITH .1 LB. QUINHYDRONE/l-OOO GAL.

Nil 2. 3

Nil 2. 0 N il 2. 0 Nil 4. 2 Nil 4. 4

7. 1 0. 9 Trace 9. 2 Trace 4. 0

These tests show that whereas, without inhibitor (tests Nos 1218), theleaded fuel formed a yellow or brown precipitatein the acceleratedleaded isopentane is unstable in respect to formation of a precipitatecontaining lead during storage, this instability is overcome by theaddition of hydroquinone or quinhydrone as shown in the tests set forthin Table 3 involving a 100- octane fuel containing 7.2 isopentane and 3cc. of tetraethyl lead.

Although the invention is intended to apply primarily to fuels whosehydrocarbon base stock is composed substantially or entirely ofaliphatic hydrocarbons, either natural or synthetic, with or withoutaddition of various anti-knock agents which are oiwgenated or othertypes of derivatives of hydrocarbons, in its broader sense the inventionalso comprises blends of such relatively pure aliphatic base stocks withminor amounts of aromatic-containing petroleum fractions in such low ornon-stabilizing proportions that the mixed fuel blend when leaded isstill normally unstable in respect to formation of a precipitatecontaining lead during storage.

It is not intended that this invention be unnecessarily limited by anytheory suggested as to the mechanism of the operation of the inventionnor by any of the specific examples which have been given merely for thesake of illustration, but only by the appended claims in which it isintended to claim all novelty inherent in the invention as well as allmodifications coming within the spirit and scope of the invention.

I claim:

1. A motor fuel comprising a hydrocarbon mixture normally stable againstgum formation and composed predominately of saturated aliphatichydrocarbons and containing a small amount of a lead alkyl anti-knockagent which in the presence of said hydrocarbons tends during storage toform lead-containing precipitates and a hydrox aromatic hydrocarbon ofthe class consisting of hydroquinon and quinhydrone in an amountsufficient to inhibit the formation of a lead-containing precipitateduring storage.

2. Motor fuel according to claim 1 in which the 10 hydrocarbon fuel basestock has an octane number of at least 80.

3. Motor fuel according to claim 1 in which the hydrocarbon fuel basestock consists entirely of saturated aliphatic hydrocarbons and withouttetraethyl lead is normally stable against precipitate and gum formationduring storage.

4. Motor fuel according to claim 1 containing at least 3 cc. oftetraethyl lead per gallon of fuel.

5. A motor fuel comprising a lead alkyl antiknock agent and ahydrocarbon base stock which is normally stable against precipitate andgum formation during storage in the absence of lead alkyl compounds,said hydrocarbon base stock consisting substantially entirely ofsynthetic liquid hydrocarbons within the gasoline boiling range made byalkylation of normal olefins with isoparaifins, together with a smallamount of wturated C5 hydrocarbon to obtain the desired vapor pressure,said fuel being stabilized against deterioration during storage byhaving added thereto a small amount of hydroquinone.

6. Motor fuel according to claim 5 in which the alkylate base stock ismade by alkylation of an olefin selected from the group consisting ofbutylenes and pentylenes with isobutane, and the fuel contains at least3 cc. of tetraethyl lead and about .05-0.5 lb. of hydroquinone per 1000gallons of fuel.

7. A motor fuel comprising a lead alkyl antiknock agent and ahydrocarbon base stock which is normally stable against precipitate andgum formation during storage in the absence of lead alkyl compounds,said hydrocarbon base stock comprising a hydrogenated copolymer of anormal olefin having from 2 to 6 carbon atoms and an iso-olefin having 4to 5 carbon atoms, said fuel being stabilized against deteriorationduring storage by having added thereto a small amount of hydroquinone.

PAUL L. DE VERTER.

